1. Field of the Invention
The present invention relates generally to nanofabrication techniques, and more particularly to a method for fabricating sub-50 nanometer imprint molds.
2. Description of Related Art
Advancements in nanotechnology have generated a need for fabrication of sub-50 nanometer (nm) structures and devices. Generally, techniques used for fabrication the sub-50 nanometer devices and structures include conventional top-down and bottom-up approaches. However, these approaches have significant limitation of patterning the fabricated feature with control.
As such, nanofabrication technique including, for example, nanoimprint lithography, has been used to produce high-throughput, controllable features. Nanoimprint lithography is a technique based on mechanical embossing, i.e., indirect pattern transfer on a target substrate or film. Nanoimprint lithography can give higher resolutions overcoming conventional lithographic light diffraction and beam scattering problems.
Generally, in nanoimprint lithography, a mold is made with the desired feature size and pattern on one side of the mold. The patterned side is subsequently embossed on a polymer coating over a target substrate. This is done under controlled temperature and pressure. After embossing, the mold is removed and the pattern is transferred onto a polymer. Next, a highly selective reactive ion etching is done to create a shallow trench, which eventually creates sub-50 nm features on the desired target.
However, the resolution of nanofabrication using the nanoimprint technique has numerous constraints. For example, fabricating masters with small features using conventional photolithography is not feasible due to the constraints of the wavelengths used. Additionally, problems such as the ability of a material to mold with high repeatability and efficiency may be lacking due to the nature of the materials used. Other examples of deficiencies of current techniques include the distortion of features in the transferred pattern, the swelling of the master by the monomers used or the solvent used to dissolve polymers, and the ability of a molded material to fill a mold completely.
Other techniques such as high resolution patterning are using electron or ion beam lithography, soft pattern transfer, microcontact printing, scanning probe lithography, edge lithography, or self-assembly for nanofabrication. However, all these techniques are still in research and development phases, and thus, may not be feasible for high throughput, commercial usage.
For example, in high-resolution electron or ion beam patterning, to increase resolution requires decreasing the diameter of particle beam, and thus, decreases the beam current. The changes to the particle beam increase the time necessary to achieve the same imaging dose.
Microcontact printing also has constraints such as failing to achieve the minimum size of features in stamps, lateral dimensions, and resolution of the transferred material. Additionally, the preferential adhesion of a printed material on a second surface uses current photolithography techniques, which may cause defects.
Scanning probe lithography is a serial writing process, which is inherently slow. Therefore, the use of scanning probe lithography is mostly research oriented. Also, scanning probe lithography is challenging to generate reproducible structures between scans because of variations in the surface topography of the substrate and differences in the shape of the tip.
Edge lithography can be limited in its ability to pattern arbitrary features due to the characteristics of light. Also, patterning intersecting lines of metal layers using edge lithography is method is a complicated, time consuming process.
Self-assembly techniques are currently unable to produce structures with precise spatial positioning and arbitrary shapes with a low concentration of defects and functionality. It is also unable to generate range patterns required for even simple electron functionality.
Any shortcoming mentioned above is not intended to be exhaustive, but rather is among many that tends to impair the effectiveness of previously known techniques for fabricating nanoscale features; however, shortcomings mentioned here are sufficient to demonstrate that the methodologies appearing in the art have not been satisfactory and that a significant need exists for the techniques described and claimed in this disclosure.